First-principles supercell studies of the substitutional carbon in c-BN

The effects of hydrostatic pressure on the formation enthalpy and electronic level positions of C N and C B in c-BN are investigated by means of ab initio plane-wave pseudopotential method using a supercell approach in the range of 0–60 GPa. The formation enthalpy decreases with pressure for C B, suggesting that C B becomes much more stable and has a larger concentration with pressure increase. In contrast to C B, the C N impurity exhibits positive dependence of the formation enthalpy on pressure, so the concentration of C N reduces with pressure. With pressure increase, the defect energy levels of C B + 1 and C N – 1 move into the conduction band and the valence band, respectively, while the defect energy levels of C B and C N in other charge states all move toward the center of band gap. These results suggest that pressure may make electron transfer between the impurity band and the conduction band or the valence band difficult and weaken its conductivity when a C atom substitutes at a B site or at a N site in c-BN.